![]() ![]() The “earthy” end (moving vanes and spindle) is connected to the 22pF capacitor C1. The tunning capacitor VC1 is one of the two fm sections of a miniature fm transistor radio with built-in trimmers (VC2). Transistors List TR1 = BF199 TR2 = TR3 = TR4 = BC547 After that L1 should be stretched carefully and evenly to a length of about 13mm. Coil L1 is formed by winding 8 turns of 1mm (20 swg) enamelled copper wire on a 6 mm diameter former, which is then removed. The critical part of the fm radio receiver is the first stage, TR1/VC1, where the wirings must be kept as short as possible. In some areas 3 stages of audio amplification may not be necessary, in which case TR3 and its associated components can be omitted and the free end of capacitor C5 connected to the collector of TR2. And I m still trying hoping one day I will found a working one and this general design helps me alot in constructing various new variants.īelow I will show u several circuit designs made by several hobbyists, which I redrawn and omitted the audio amplifier part to enable easy matching with the general circuit proposed before.This simple fm radio receiver circuit consists of a regenerative rf stage, TR1, followed by a two of three-stage audio amplifier, TR2 to TR4. To be honest, I ve tried various FM single transistor designs but none of them worked. It enables everyone to even create their own variants of FM single transistor receiver. ![]() ![]() Their values are again, designers' choices.īy using this generalised circuit, anyone can play with various choice of values of any of the involved components, coils and transistors without being restricted to the designs proposed on the internet. ![]() The length of the antenna, and the position of tap are the designer's choices.ĩ) Coil: the number of turns, the length and the diameter are all designer's choices.ġ0), 11) and 12) are capacitor and resistors to regulate the power supply. The position where the feedback capacitor taps is designer's choice.Ĩ) Antenna and antenna's tap points: antenna touches the coil at the antenna's tap points. This capacitor taps the coil at (7) to form a regenerative topology.ħ) Capacitor's tap points: Part of the coil where the feedback capacitor touches. Various kinds of choke are made depending on the designers' choices.Ĥ) Resistor: The value of the resistor can be adjusted to obtain the most clear audio output.Ħ)Feedback capacitor: Its value is also designer's choice. It can be home-made, by just winding copper wire around a cylindrical air core or ferrite torroid. Here are the examples: MPF102 (frequently used), BF245, J310 ( is now obsolete), 2N4416, RS2003 (Radio Shack JFET), 2N3819, BF256.ģ) RF choke: The purpose of RF choke is to block high frequency signal from reaching the audio amplifier. For FM receiver, the corresponding resonant frequency must be within 80 to 108 MHz.Ģ) The JFET transistor: From analysis I found out collections of transistor types suitable for the operation. The value of the capacitors much be carefully chosen cuz it will determine the bandwidth within where the circuit will resonate. So this part depends on the designer's choice. Now I am going to explain each part of the circuit, each numbered point below refers to corresponding red circled number in the diagram:ġ) Group of capacitors: Some of the designs use capacitors arranged only parallely, while others just in series. But like I said, most of it follow the above configuration. Most of single transistor FM radio receiver circuits I found on the internet dont deviate much from the above generalised design,except few which are completely different from it. FM radio receiver using just one JFET transistor as an active non linear element, in regenerative topology. ![]()
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